This deterioration, furthermore, varies substantially by income and race, and its impact persists even past childhood. Barbara Heyns, a sociologist at New York University who studied Atlanta schoolchildren in the late 1970s, found that although academic gains during the school year were not substantially correlated with income, summer decline was.
Subsequent studies have replicated the finding. Karl Alexander, Doris Entwisle and Linda Olson of Johns Hopkins University, for example, found that the summer fade can largely explain why the gap in skills between children on either side of the socioeconomic divide widens as students progress through elementary school. Children from all backgrounds learn at similar rates during the school year, but each summer students of high socioeconomic status continue to learn while those of low socioeconomic status fall behind.
The impact is felt even years later. The learning differences that begin in grade school "substantially account" for differences by socioeconomic status in high-school graduation rates and in four-year college attendance, Alexander and his co-authors report.
The summer increase in children's body-mass index has also been measured. In one study, Paul T. von Hippel, a sociologist then at Ohio State University, and his co-authors found that the average monthly gain in BMI for students moving from kindergarten to first grade was two to three times as fast during the summer as during either of the adjoining academic years. And the children most prone to obesity were most likely to put on additional weight during the summer.
So what can we do to fight summer learning loss and weight gain and restore the season's halcyon reputation?
Let's start with the most ambitious option: lengthening the school year. I have written previously about the benefit of extending the hours of the school day. A similar argument applies to extending the academic year: More time at task helps children learn, and it would be worth the extra expense involved.
The second option is an idea proposed several years ago by Alan Krueger, now the chairman of President Barack Obama's Council of Economic Advisers, and Molly Fifer, then a graduate student in economics at Princeton University: Offer students in kindergarten through fifth grade who qualify for free meals through the National School Lunch Program the opportunity to participate in a six-week summer enrichment program that would be focused on small-group instruction. Krueger and Fifer estimated that such a program would cost less than $2,000 per student. If the federal government paid half, the cost to taxpayers would be about $2 billion a year, and the benefits would be worth much more.
Some educators are not waiting for the federal government to act – which appears to be wise, given the inertia in a polarized Washington. For example, the National Summer Learning Association, with private funding, recently began a three-year "Smarter Summers" initiative in 10 cities, aimed at providing high-quality summer instruction for 20,000 students.
The third and least ambitious option is to provide voluntary summer reading programs for students of low socioeconomic status. A randomized experiment conducted by James Kim of Harvard University and Thomas White of the University of Virginia showed that students developed better reading skills when they were provided with books during the summer and encouragement from teachers before the break began.
A voluntary summer reading program need not be expensive. Yet it's not enough to merely give children books; encouragement from teachers and parents is also crucial. And for some students, even that may not be sufficient; in another study, Kim and Jonathan Guryan, then at the University of Chicago, found that a reading program for low-income, Spanish-speaking Latino children provided no measurable benefit in reading comprehension or vocabulary.
July should be a time of activity – for children and for lawmakers. When Congress finally gets around to considering the reauthorization of the Elementary and Secondary Education Act, it should include an aggressive program to reverse summer learning loss. Don't bet on Congress fulfilling that assignment this year, but we should hold them to it before school is out for the summer of 2013.
Peter Orszag is vice chairman of global banking at Citigroup Inc. and a former director of the Office of Management and Budget in the Obama administration.